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Abstract:

A partial discharge sensor evaluation method includes a first frequency
characteristic measuring process in which, in a state where a reference
antenna 3 for which a frequency characteristic in an effective height is
known and a measuring antenna 2 are installed on a flat ground 1 to be
separated by a predetermined distance from each other, a transmission
characteristic measurer 4 measures a frequency characteristic of a
transmission characteristic between the reference antenna 3 and the
measuring antenna 2, and a second frequency characteristic measuring
process in which, in a state where a measured antenna 9 is installed
inside a cylindrical ground 6 buried in a circular opening 5 formed at a
position where the reference antenna 3 has been installed, the
transmission characteristic measurer 4 measures the frequency
characteristic of the transmission characteristic between the measured
antenna 9 and the measuring antenna 2.

Claims:

1. A partial discharge sensor evaluation method comprising: a first
frequency characteristic measuring process in which, in a state where a
reference antenna for which a frequency characteristic in an effective
height is known and a measuring antenna are installed on a flat ground to
be separated by a predetermined distance from each other, a transmission
characteristic measurer measures a frequency characteristic of a
transmission characteristic between the reference antenna and the
measuring antenna; a second frequency characteristic measuring process in
which, in a state where the reference antenna is removed, and a measured
antenna is installed inside a cylindrical ground buried in a circular
opening formed at a position where the reference antenna has been
installed, the transmission characteristic measurer measures the
frequency characteristic of the transmission characteristic between the
measured antenna and the measuring antenna; and a calculation process in
which a calculation apparatus calculates the frequency characteristic in
an effective height of the measured antenna based on the frequency
characteristic of the transmission characteristic measured in the first
frequency characteristic measuring process and the frequency
characteristic of the transmission characteristic measured in the second
frequency characteristic measuring process.

2. The partial discharge sensor evaluation method according to claim 1,
wherein in the calculation process, the frequency characteristic in the
effective height of the measured antenna is calculated based on the
frequency characteristic of the transmission characteristic measured in
the first frequency characteristic measuring process and the frequency
characteristic of the transmission characteristic measured in the second
frequency characteristic measuring process, and a frequency average value
in the effective height is also calculated.

3. The partial discharge sensor evaluation method according to claim 1,
wherein, in the first frequency characteristic measuring process, in a
state where a plurality of the measuring antennas are arranged around the
reference antenna, the transmission characteristic measurer measures the
frequency characteristic of the transmission characteristic between the
reference antenna and the plurality of measuring antennas, in the second
frequency characteristic measuring process, the transmission
characteristic measurer measures the frequency characteristic of the
transmission characteristic between the measured antenna and the
plurality of measuring antennas, and in the calculation process, an
electric field at a point separated by a predetermined distance or longer
from the reference antenna is calculated based on the frequency
characteristic of the transmission characteristic measured in the first
frequency characteristic measuring process, and also the electric field
at the point separated by the predetermined distance or longer from the
measured antenna is calculated based on the frequency characteristic of
the transmission characteristic measured in the second frequency
characteristic measuring process, and the frequency characteristic in the
effective height of the measured antenna is calculated based on the
electric fields at both the points.

4. The partial discharge sensor evaluation method according to claim 3,
wherein in the calculation process, the frequency characteristic in the
effective height of the measured antenna is calculated based on the
electric fields at both the points, and a frequency average value in the
effective height is also calculated.

5. A partial discharge sensor evaluation method comprising: a first
frequency characteristic measuring process in which, in a state where a
reference antenna for which a frequency characteristic in an effective
height is known and a measuring antenna are installed on a flat ground to
be separated by a predetermined distance from each other, a transmission
characteristic measurer measures a frequency characteristic of a
transmission characteristic between the reference antenna and the
measuring antenna; a second frequency characteristic measuring process in
which, when the reference antenna is removed, and there are provided: a
dielectric plate in which opposite ends in a longitudinal side of a
slit-like opening that is formed at a position where the reference
antenna has been installed are set as opposite end portions in a width
direction and which has a central portion that is buried in the slit-like
opening; and two conductor plates arranged so as to sandwich the
dielectric plate and each electrically connected to ground at one end, in
a state where a measured antenna is installed on the dielectric plate,
the transmission characteristic measurer measures the frequency
characteristic of the transmission characteristic between the measured
antenna and the measuring antenna; and a calculation process in which a
calculation apparatus calculates the frequency characteristic in an
effective height of the measured antenna based on the frequency
characteristic of the transmission characteristic measured in the first
frequency characteristic measuring process, and the frequency
characteristic of the transmission characteristic measured in the second
frequency characteristic measuring process.

6. The partial discharge sensor evaluation method according to claim 5,
wherein in the calculation process, the frequency characteristic in the
effective height of the measured antenna is calculated based on the
frequency characteristic of the transmission characteristic measured in
the first frequency characteristic measuring process and the frequency
characteristic of the transmission characteristic measured in the second
frequency characteristic measuring process, and a frequency average value
in the effective height is also calculated.

7. The partial discharge sensor evaluation method according to claim 5,
wherein, in the first frequency characteristic measuring process, in a
state where a plurality of the measuring antennas are arranged around the
reference antenna, the transmission characteristic measurer measures the
frequency characteristic of the transmission characteristic between the
reference antenna and the plurality of measuring antennas, in the second
frequency characteristic measuring process, the transmission
characteristic measurer measures the frequency characteristic of the
transmission characteristic between the measured antenna and the
plurality of measuring antennas, and in the calculation process, an
electric field at a point separated by the predetermined distance or
longer from the reference antenna is calculated based on the frequency
characteristic of the transmission characteristic measured in the first
frequency characteristic measuring process, and also the electric field
at the point separated by the predetermined distance or longer from the
measured antenna is calculated based on the frequency characteristic of
the transmission characteristic measured in the second frequency
characteristic measuring process, and the frequency characteristic in the
effective height of the measured antenna is calculated based on the
electric fields at both the points.

8. The partial discharge sensor evaluation method according to claim 7,
wherein in the calculation process, the frequency characteristic in the
effective height of the measured antenna is calculated based on the
electric fields at both the points, and a frequency average value in the
effective height is also calculated.

9. A partial discharge sensor evaluation apparatus comprising: a
measuring antenna installed on a flat ground; a reference antenna which
is installed on the flat ground to be separated by a predetermined
distance from the measuring antenna, and for which a frequency
characteristic in an effective height is known; a cylindrical ground in
which the reference antenna is removed, and which is buried in a circular
opening formed at a position where the reference antenna is has been
installed; a measured antenna installed inside the cylindrical ground; a
transmission characteristic measurer that measures the frequency
characteristic of a transmission characteristic between the reference
antenna and the measuring antenna and also that measures the frequency
characteristic of the transmission characteristic between the measured
antenna and the measuring antenna; and a calculation apparatus that
calculates the frequency characteristic in the effective height of the
measured antenna based on the frequency characteristics of both the
transmission characteristics measured by the transmission characteristic
measurer.

10. The partial discharge sensor evaluation apparatus according to claim
9, wherein a plurality of the measuring antennas is arranged around a
position where the reference antenna and the measured antenna are
installed, the transmission characteristic measurer measures the
frequency characteristic of the transmission characteristic between the
reference antenna and the plurality of measuring antennas, and also
measures the frequency characteristic of the transmission characteristic
between the measured antenna and the plurality of measuring antennas, and
the calculation apparatus calculates an electric field at a point
separated by the predetermined distance or longer from the reference
antenna based on the frequency characteristic of the transmission
characteristic between the reference antenna and the plurality of
measuring antennas measured by the transmission characteristic measurer,
and also calculates the electric field at the point separated by the
predetermined distance or longer from the measured antenna based on the
frequency characteristic of the transmission characteristic between the
measured antenna and the plurality of measuring antennas measured by the
transmission characteristic measurer, and calculates the frequency
characteristic in the effective height of the measured antenna based on
the electric fields at both the points.

11. The partial discharge sensor evaluation apparatus according to claim
9, wherein a radio wave absorber is installed or applied around the flat
ground.

12. The partial discharge sensor evaluation apparatus according to claim
9, wherein a cut is provided on an edge portion at a periphery of the
flat ground.

13. The partial discharge sensor evaluation apparatus according to claim
9, wherein an edge portion at a periphery of the flat ground is curved
toward a side opposite to the measuring antenna.

14. A partial discharge sensor evaluation apparatus comprising: a
measuring antenna installed on a flat ground; a reference antenna which
is installed on the flat ground to be separated by a predetermined
distance from the measuring antenna, and for which a frequency
characteristic in an effective height is known; a dielectric plate in
which after removal of the reference antenna, opposite ends in a
longitudinal side of a slit-like opening that is formed at a position
where the reference antenna has been installed are set as opposite end
portions in a width direction and which has a central portion that is
buried in the slit-like opening; two conductor plates arranged so as to
sandwich the dielectric plate and each electrically connected to ground
at one end; a measured antenna installed on the dielectric plate; a
transmission characteristic measurer that measures the frequency
characteristic of a transmission characteristic between the reference
antenna and the measuring antenna, and also that measures the frequency
characteristic of the transmission characteristic between the measured
antenna and the measuring antenna; and a calculation apparatus that
calculates the frequency characteristic in the effective height of the
measured antenna based on the frequency characteristics of both the
transmission characteristics measured by the transmission characteristic
measurer.

15. The partial discharge sensor evaluation apparatus according to claim
14, wherein a plurality of the measuring antennas are arranged around the
position where the reference antenna and the measured antenna are
installed, the transmission characteristic measurer measures the
frequency characteristic of the transmission characteristic between the
reference antenna and the plurality of measuring antennas, and also
measures the frequency characteristic of the transmission characteristic
between the measured antenna and the plurality of measuring antennas, and
the calculation apparatus calculates an electric field at a point
separated by the predetermined distance or longer from the reference
antenna based on the frequency characteristic of the transmission
characteristic between the reference antenna and the plurality of
measuring antennas measured by the transmission characteristic measurer,
and also calculates the electric field at the point separated by the
predetermined distance or longer from the measured antenna based on the
frequency characteristic of the transmission characteristic between the
measured antenna and the plurality of measuring antennas measured by the
transmission characteristic measurer, and calculates the frequency
characteristic in the effective height of the measured antenna based on
the electric fields at both the points.

16. The partial discharge sensor evaluation apparatus according to claim
14, wherein a radio wave absorber is installed or applied around the flat
ground.

17. The partial discharge sensor evaluation apparatus according to claim
14, wherein a cut is provided on an edge portion at a periphery of the
flat ground.

18. The partial discharge sensor evaluation apparatus according to claim
14, wherein an edge portion at a periphery of the flat ground is curved
toward a side opposite to the measuring antenna.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a partial discharge sensor
evaluation method and a partial discharge sensor evaluation apparatus to
be used when detecting a high frequency generated in an apparatus in a
high power facility such as a GIS (Gas Insulated Switchgear) to detect a
partial discharge phenomenon.

[0003] Upon receiving a high frequency generated by a signal source 101, a
G-TEM cell 102 converts the high frequency into a substantially plane
wave, and propagates the plane wave.

[0004] Thus, a partial discharge sensor 103 is irradiated with a polarized
wave perpendicular to a metal surface on which the sensor is installed.

[0005] A digitizer 104 compares the intensity of a radio wave received by
the partial discharge sensor 103 with that of the high frequency
generated by the signal source 101 to measure a transmission
characteristic from the signal source 101 to the partial discharge sensor
103.

[0006] Further, when a reference antenna with a known effective height of
antenna is installed instead of the partial discharge sensor 103, the
digitizer 104 measures a transmission characteristic from the signal
source 101 to the reference antenna.

[0007] It is possible to determine the effective height of antenna of the
partial discharge sensor 103 when the transmission characteristic from
the signal source 101 to the partial discharge sensor 103 is compared
with the transmission characteristic from the signal source 101 to the
reference antenna.

[0008] Furthermore, it is possible to determine a frequency characteristic
in the effective height of antenna when a similar measurement is
performed while the frequency of the signal source 101 is varied, and a
value in which these frequency characteristics are averaged at a
prescribed frequency is generally used as an index for the partial
discharge sensor 103.

[0010] The conventional partial discharge sensor evaluation apparatus is
configured as mentioned above, and thus, the effective height of antenna
of the partial discharge sensor 103 can be determined. However, the G-TEM
cell 102 has a large size exceeding 3 m, which increases the size of the
whole apparatus; consequently, there is a problem such that the apparatus
is constrained in terms of an installation site and the like.

[0011] The present invention has been made in order to solve the
above-described problem, and an object of the invention is to provide a
partial discharge sensor evaluation method and a partial discharge sensor
evaluation apparatus that can achieve reduction in size of the whole
apparatus.

Means for Solving the Problems

[0012] A partial discharge sensor evaluation method according to the
present invention includes: a first frequency characteristic measuring
process in which, in a state where a reference antenna for which a
frequency characteristic in an effective height is known and a measuring
antenna are installed on a flat ground to be separated by a predetermined
distance from each other, a transmission characteristic measurer measures
a frequency characteristic of a transmission characteristic between the
reference antenna and the measuring antenna; a second frequency
characteristic measuring process in which, in a state where the reference
antenna is removed, and a measured antenna is installed inside a
cylindrical ground buried in a circular opening formed at a position
where the reference antenna has been installed, the transmission
characteristic measurer measures the frequency characteristic of the
transmission characteristic between the measured antenna and the
measuring antenna; and a calculation process in which a calculation
apparatus calculates the frequency characteristic in an effective height
of the measured antenna based on the frequency characteristic of the
transmission characteristic measured in the first frequency
characteristic measuring process and the frequency characteristic of the
transmission characteristic measured in the second frequency
characteristic measuring process.

Effect of the Invention

[0013] According to the present invention, there is an advantageous effect
such that the frequency characteristic in the effective height of the
measured antenna can be calculated without the use of a large G-TEM cell
to thereby achieve reduction in size of the whole apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a flowchart depicting a partial discharge sensor
evaluation method according to Embodiment 1 of the present invention.

[0015] FIG. 2 is a diagram illustrating a state where a measuring antenna
2 and a reference antenna 3 are installed on a flat ground 1.

[0016] FIG. 3 is a diagram depicting a state where a cylindrical ground 6
in which a measured antenna 9 is installed is buried in a circular
opening 5.

[0030] FIG. 1 is a flowchart illustrating a partial discharge sensor
evaluation method according to Embodiment 1 of the present invention.

[0031] FIG. 2 is a diagram illustrating a state where a measuring antenna
2 and a reference antenna 3 are installed on a flat ground 1.

[0032] In FIG. 2, the flat ground 1 is a metal plate on which the
measuring antenna 2 and the reference antenna 3 are to be installed.

[0033] The measuring antenna 2 is formed of, for example, a monopole
antenna and installed on the flat ground 1.

[0034] The monopole antenna radiates a high frequency in a plane
orthogonal to a longitudinal direction of the monopole antenna (side
direction) when the length of the monopole antenna is equal to or smaller
than a half wavelength. A measured antenna 9 described below (see FIG. 5)
is installed in the side direction of the measuring antenna 2 that is the
monopole antenna, and thus, the length of the monopole antenna is set to
be equal to or smaller than the half wavelength of a maximum frequency to
be measured.

[0035] The reference antenna 3 is the antenna for which a frequency
characteristic in an effective height of antenna heff_ref(f) is known,
and is installed to be separated by a predetermined distance from the
measuring antenna 2.

[0036] Additionally, any antenna may be employed for the reference antenna
3 as long as the effective height of antenna heff_ref(f) is known;
however, as disclosed in Non-Patent Literature 1, in general, a 25-mm
monopole antenna is employed.

[0037] Measurement accuracy thereof is enhanced as the predetermined
distance (distance between the measuring antenna 2 and the reference
antenna 3) is larger.

[0038] For example, when a diameter of a circular opening 5 of the
measured antenna 9 described below to the flat ground 1 is denoted as D,
given that the predetermined distance is equal to or larger than
(D×D/wavelength), the measurement accuracy is achieved which is
equivalent to that in a case where the measuring antenna 2 and the
reference antenna 3 are sufficiently separated from each other.

[0039] A network analyzer 4 executes processing of measuring a frequency
characteristic E_ref(f) of a transmission characteristic between the
reference antenna 3 and the measuring antenna 2, and also measuring a
frequency characteristic E_dut(f) of a transmission characteristic
between the measured antenna 9 described below and the measuring antenna
2. Note that the network analyzer 4 constitutes a transmission
characteristic measurer.

[0040] A calculation apparatus 4a includes, for example, a personal
computer, and executes processing of calculating a frequency
characteristic heff(f) in the effective height of the measured antenna 9
based on the frequency characteristic E_ref(f) of the transmission
characteristic between the reference antenna 3 and the measuring antenna
2 measured by the network analyzer 4 and the frequency characteristic
E_dut(f) of the transmission characteristic between the measured antenna
9 and the measuring antenna 2 measured by the network analyzer 4, and
also calculating a frequency average value heff_average in the effective
height. Note that the calculation apparatus 4a constitutes an
effective-height-frequency characteristic calculator.

[0041] FIG. 3 is a diagram illustrating a state where a cylindrical ground
6 in which the measured antenna 9 is installed is buried in the circular
opening 5. FIG. 4 is a diagram illustrating the measured antenna 9
installed inside the cylindrical ground 6.

[0042] In addition, FIG. 5 is a diagram illustrating a state where the
measured antenna 9 is installed with the flat ground 1.

[0043] In FIGS. 3 to 5, the circular opening 5 is a circular opening part
formed at a position where the reference antenna 3 is installed.

[0044] The cylindrical ground 6 is a cylindrical metal member buried in
the circular opening 5, and a flange 7 is connected to a lower portion
thereof. Further, the flange 7 is connected to an antenna ground 8.

[0045] The measured antenna 9 is installed on the antenna ground 8 in the
cylindrical ground 6.

[0046] Next, an operation will be described.

[0047] A first frequency characteristic measuring process of steps ST1 to
ST3 will be initially described.

[0048] First, in order to measure the frequency characteristic E_ref(f) of
the transmission characteristic between the reference antenna 3 and the
measuring antenna 2, the measuring antenna 2 that is the monopole antenna
is installed on the flat ground 1 as depicted in FIG. 2 (step ST1 in FIG.
1).

[0049] Then, the reference antenna 3 for which the frequency
characteristic of the effective height of antenna heff_ref(f) is known is
installed on the flat ground 1 to be separated by the predetermined
distance from the measuring antenna 2 (step ST2).

[0050] In this regard, the predetermined distance is such a distance as
will be equal to or larger than (D×D/wavelength) given that the
diameter of the circular opening 5 is D as mentioned above.

[0051] When the reference antenna 3 and the measuring antenna 2 are
installed on the flat ground 1, the network analyzer 4 measures the
frequency characteristic E_ref(f) of the transmission characteristic
between the reference antenna 3 and the measuring antenna 2 (step ST3).

[0052] Next, a second frequency characteristic measuring process of steps
ST4 to ST6 will be described.

[0053] First, the reference antenna 3 is removed from the flat ground 1,
and then, as depicted in FIG. 3, the circular opening 5 is formed at a
position where the reference antenna 3 has been installed, and the
cylindrical ground 6 with the flange 7 connected to the lower portion
thereof is buried in the circular opening 5 (step ST4).

[0054] Then, the flange 7 of the cylindrical ground 6 is connected to the
antenna ground 8, and as depicted in FIG. 5, the measured antenna 9 is
installed on the antenna ground 8 in the cylindrical ground 6 (step ST5).

[0055] When the measured antenna 9 is installed in the cylindrical ground
6, the network analyzer 4 measures the frequency characteristic E_dut(f)
of the transmission characteristic between the measured antenna 9 and the
measuring antenna 2 (step ST6).

[0056] Next, a calculation process of steps ST7and ST8 will be described.
When the frequency characteristic E_ref(f) of the transmission
characteristic between the reference antenna 3 and the measuring antenna
2 and the frequency characteristic E_dut(f) of the transmission
characteristic between the measured antenna 9 and the measuring antenna 2
are measured, the calculation apparatus 4a calculates the frequency
characteristic heff(f) in the effective height of the measured antenna 9
by substituting the frequency characteristic E_ref(f) and the frequency
characteristic E_dut(f) into the following Expression (1) (step ST7).

[0057] In Expression (1), the heff_ref(f) designates the effective height
of antenna of the reference antenna 3.

[0058] Upon calculating the frequency characteristic heff(f) in the
effective height of the measured antenna 9, the calculation apparatus 4a
calculates the frequency average value heff_average in the effective
height as illustrated in the following Expression (2) (step ST8).

[0059] In this case, the network analyzer 4 performs a similar measurement
while the frequency of a radio wave supplied to the measuring antenna 2
(prescribed frequency) is varied, and the frequency characteristic
heff(f) in the effective height is averaged at a prescribed frequency. As
the prescribed frequency, for example, the one of 500 MHz to 1500 MHz is
used.

heff_average = 1 fH - fL ∫ fL fH heff ( f )
f ( 2 ) ##EQU00002##

[0060] The measuring antenna 2 that is the monopole antenna installed on
the flat ground 1 radiates a polarized wave perpendicular to the flat
ground 1, and a high frequency propagates along the flat ground 1.
Therefore, when the measuring antenna 2 and the measured antenna 9 are
installed as depicted in FIG. 5, the polarized wave perpendicular to the
flat ground 1 can be irradiated to a side surface of the measured antenna
9, similarly to a case where a G-TEM cell is used.

[0061] As a result, the procedure illustrated in steps ST1 to ST8 enables
an evaluation that is equivalent to that in the case where the G-TEM cell
is used.

[0062] For example, on the assumption that the diameter of the circular
opening 5 is "350 mm" and that a frequency to be observed is 500 MHz to
1500 MHz, the predetermined distance has a maximum value of "612 mm."

[0063] For this reason, the length of the flat ground 1 is within
approximately 1 m at a maximum, and thus, an evaluation facility with a
smaller installation area can be established as compared to the G-TEM
cell.

[0064] Furthermore, the G-TEM cell can be replaced with the single flat
ground 1, which enables cost reduction of the facility itself.

[0065] As is apparent from the above description, according to Embodiment
1, the frequency characteristic heff(f) in the effective height of the
measured antenna 9 and the frequency average value heff_average in the
effective height can be calculated without the use of the large G-TEM
cell, which provides an advantageous effect that can achieve reduction in
size of the whole apparatus.

Embodiment 2

[0066] FIG. 6 is a flowchart illustrating a partial discharge sensor
evaluation method according to Embodiment 2 of the present invention.

[0067] FIG. 7 is a diagram illustrating a state where a plurality of
measuring antennas 2 and a reference antenna 3 are installed on a flat
ground 1. FIG. 8 is a diagram illustrating a state where the plurality of
measuring antennas 2 and a measured antenna 9 are installed on the flat
ground 1.

[0068] In the above Embodiment 1, there is illustrated the case that the
measuring antenna 2 and the reference antenna 3 (measured antenna 9) are
installed on the flat ground 1 with separated by the predetermined
distance from each other, while in Embodiment 2, it is different from
Embodiment 1 in that the N measuring antennas 2 are arranged around the
reference antenna 3 (measured antenna 9) (disposed along a closed curve).
Note that N designates an integer of 2 or more.

[0069] A network analyzer 10 measures executes processing of measuring a
frequency characteristic E_ref_i(f) of a transmission characteristic
between the reference antenna 3 and the N measuring antennas 2, and
measuring a frequency characteristic E--dut_i(f) of a transmission
characteristic between the measured antenna 9 and the N measuring
antennas 2. Note that the network analyzer 10 constitutes a transmission
characteristic measurer.

[0070] A calculation apparatus 10a includes, for example, a personal
computer, and executes processing of calculating an electric field
E_ref(f) at a point separated by a predetermined distance or longer from
the reference antenna 3 based on the frequency characteristic E_ref_i(f)
of the transmission characteristic between the reference antenna 3 and
the N measuring antennas 2 measured by the network analyzer 10, and also
calculating an electric field E_dut(f) at the point separated by the
predetermined distance or longer from the measured antenna 9 based on the
frequency characteristic E_dut_i(f) of the transmission characteristic
between the measured antenna 9 and the N measuring antennas 2.

[0071] In addition, the calculation apparatus 10a executes processing of
calculating a frequency characteristic heff(f) in an effective height of
the measured antenna 9 based on the electric fields E_ref(f) and E_dut(f)
at both the points, and also calculating a frequency average value
heff_average in the effective height. Note that the calculation apparatus
10a constitutes an effective-high-frequency characteristic calculator.

[0072] Next, an operation will be described.

[0073] A first frequency characteristic measuring process of steps ST11 to
ST13 will be initially described.

[0074] First, in order to measure a frequency characteristic E_ref(f) of a
transmission characteristic between the reference antenna 3 and the
measuring antenna 2, the N measuring antennas 2 that are monopole
antennas are installed on the flat ground 1 along the closed curve as
depicted in FIG. 7 (step ST11 in FIG. 6).

[0075] Then, the reference antenna 3 for which a frequency characteristic
in the effective height of antenna heff_ref(f) is known is installed at
any position in the closed curve (step ST12).

[0076] In this manner, the N measuring antennas 2 may be arranged around
the reference antenna 3.

[0077] When the reference antenna 3 and the N measuring antennas 2 are
installed on the flat ground 1, the network analyzer 10 measures the
frequency characteristic E_ref_i(f) of the transmission characteristic
between the reference antenna 3 and the N measuring antennas 2 while the
measuring antenna 2 to be measured is switched among the N measuring
antennas 2 by a switch (step ST13). Here, i=1, 2, . . . , N.

[0078] Next, a second frequency characteristic measuring process of steps
ST14 to ST16 will be described.

[0079] Similarly to the above Embodiment 1, the reference antenna 3 is
removed from the flat ground 1, a circular opening 5 is formed at a
position where the reference antenna 3 has been installed, and a
cylindrical ground 6 with a flange 7 connected to a lower portion thereof
is buried in the circular opening 5 (step ST14).

[0080] Then, the flange 7 of the cylindrical ground 6 is connected to an
antenna ground 8, and the measured antenna 9 is installed on the antenna
ground 8 in the cylindrical ground 6 (step ST15).

[0081] When the measured antenna 9 is installed in the cylindrical ground
6, the network analyzer 10 measures a frequency characteristic
E--dut_i(f) of a transmission characteristic between the measured
antenna 9 and the N measuring antennas 2 while the measuring antenna 2 to
be measured is switched among the N measuring antennas 2 by the switch
(step ST16). Here, i=1, 2, . . . , N.

[0082] Next, a calculation process of steps ST17 to ST20 will be
described. Upon measuring the frequency characteristic E_ref_i(f) of the
transmission characteristic between the reference antenna 3 and the N
measuring antennas 2, and the frequency characteristic E_dut_i(f) of the
transmission characteristic between the measured antenna 9 and the N
measuring antennas 2, the calculation apparatus 10a calculates the
electric field E_ref(f) at the point separated by the predetermined
distance or longer from the reference antenna 3 (corresponding to the
left side of Expression (3)) based on the frequency characteristic
E--ref_i(f) of the transmission characteristic between the reference
antenna 3 and the N measuring antennas 2 as shown in the following
Expression (3) (step ST17).

R: Distance between the position of the measuring antenna and the
position of an observation point

[0083] k: 2π/wavelength

[0084] Note that the distance R is the distance between the coordinates of
each measuring antenna 2 and the coordinates of the observation point set
at a sufficiently longer distance from the reference antenna 3 as
compared to D2/λ. D designates the size of the measuring
antenna 2, and λ designates a wavelength. A vector n is a normal
vector which is present in the plane of the flat ground 1 and which is
directed outward with respect to the above closed curve.

[0085] Furthermore, the calculation apparatus 10a calculates the electric
field E_dut(f) at the point separated by the predetermined distance or
longer from the measured antenna 9 (corresponding to the left side of
Expression (4)) based on the frequency characteristic E_dut_i(f) of the
transmission characteristic between the measured antenna 9 and the N
measuring antennas 2 as shown in the following Expression (4) (step
ST18).

R: Distance between the position of the measuring antenna and the
position of the observation point

[0086] k: 2π/wavelength

[0087] Note that the distance R is the distance between the coordinates of
each measuring antenna 2 and the coordinates of the observation point set
at the sufficiently longer distance from the measured antenna 9 as
compared to D2/λ. D designates the size of the measuring
antenna 2, and λ designates the wavelength. The vector n is the
normal vector which is present in the plane of the flat ground 1 and
which is directed outward with respect to the above closed curve.

[0088] Upon calculating the electric fields E_ref(f) and E_dut(f) at both
the points, the calculation apparatus 10a calculates the frequency
characteristic heff(f) in the effective height of the measured antenna 9
by substituting the electric fields E_ref(f) and E_dut(f) at both the
points into the above Expression (1) (step ST19).

[0089] Upon calculating the frequency characteristic heff(f) in the
effective height of the measured antenna, the calculation apparatus 10a
calculates the frequency average value heff_average in the effective
height as shown in the above Expression (2) (step ST20).

[0090] In this case, a similar measurement is performed by the network
analyzer 10 and the calculation apparatus 10a while the frequency of a
radio wave supplied to the measuring antenna 2 (prescribed frequency) is
varied, and the frequency characteristic heff(f) in the effective height
is averaged at the prescribed frequency. As the prescribed frequency, for
example, the one of 500 MHz to 1500 MHz is used.

[0091] Performing the above steps ST11 to ST20 enables an evaluation that
is equivalent to that in a case where the G-TEM cell is used.

[0092] In Embodiment 2, the N measuring antennas 2 arranged around the
measured antenna 9 are used to calculate an equivalent far field, thus
calculating a transmission characteristic corresponding to a case where
the measured antenna element 9 and the measuring antenna 2 are
sufficiently distant from each other; consequently, the distance between
the measured antenna element 9 and the measuring antenna 2 can be
reduced. As a result, it is possible to achieve further reduction in size
of the apparatus as compared to the above Embodiment 1.

Embodiment 3

[0093] FIG. 9 is a flowchart illustrating a partial discharge sensor
evaluation method according to Embodiment 3 of the present invention.

[0094] FIG. 10(a) depicts a state of a side where a measuring antenna 2 is
installed. FIG. 10(b) is a drawing corresponding to FIG. 10(a) as viewed
from the back and depicting a state of a side where a measured antenna 16
is installed.

[0095] A state before the measured antenna 16 is installed, in other
words, a state where a reference antenna 3 is measured, is similar to
that of the above Embodiment 1 and corresponds to that of FIG. 2.

[0096] In FIG. 10, a slit-like opening 11 is a slit-like opening part
formed at a position where the reference antenna 3 has been installed.

[0097] A dielectric plate 12 is a member corresponding to an insulating
spacer 23 in FIG. 11 described below. The dielectric plate 12 is a
semi-cylindrical member that has opposite end portions located at
opposite ends of the slit-like opening 11 and a central portion buried in
the slit-like opening 11.

[0098] Conductor plates 13, 14 are members corresponding to flanges 24, 25
in FIG. 11 described below. The conductor plates 13, 14 are arranged to
sandwich the dielectric plate 12 and are each electrically connected to
ground at one end.

[0099] Bolts 15 are members corresponding to bolts 26 in FIG. 11 described
below.

[0100] The measured antenna 16 corresponds to a measured antenna 27 in
FIG. 11 described below and is installed on the dielectric plate 12.

[0101] FIG. 11 is a perspective view depicting a high-voltage electric
line installed in a GIS.

[0102] In FIG. 11, an external conductor 22 is a cylindrical member that
covers a high-voltage wire 21 and is sealed with a gas having a high
insulating property.

[0103] The insulating spacer 23 is provided at a predetermined interval in
order to hold the high-voltage wire 21, and held with a plurality of
bolts 26 with sandwiched between two flanges 24, 25.

[0104] The measured antenna 27 is installed to detect a high frequency
having propagated to the exterior through the insulating spacer 23.

[0105] FIG. 10 corresponds to a portion obtained by cutting out, with a
rectangle, the insulating spacer 23 and the flanges 24, 25 in FIG. 11.

[0106] The partial discharge sensor evaluation apparatus in Embodiment 3
simulates detection of the high frequency having propagated to the
exterior through the insulating spacer 23 in the high-voltage electric
line installed in the GIS in FIG. 11.

[0107] Next, an operation will be described.

[0108] A first frequency characteristic measuring process including steps
ST21 to ST23 will be initially described.

[0109] First, similarly to the above Embodiment 1, in order to measure a
frequency characteristic E_ref(f) of a transmission characteristic
between the reference antenna 3 and the measuring antenna 2, the
measuring antenna 2 that is a monopole antenna is installed on a flat
ground 1 as depicted in FIG. 2 (step ST21 in FIG. 9).

[0110] Then, similarly to the above Embodiment 1, the reference antenna 3
for which a frequency characteristic in an effective height of antenna
heff_ref(f) is known is installed on the flat ground 1 to be separated by
a predetermined distance from the measuring antenna 2 (step ST22).

[0111] When the reference antenna 3 and the measuring antenna 2 are
installed on the flat ground 1, the network analyzer 4 measures the
frequency characteristic E_ref(f) of the transmission characteristic
between the reference antenna 3 and the measuring antenna 2, similarly to
the above Embodiment 1 (step ST23).

[0112] Next, a second frequency characteristic measuring process of steps
ST24 to ST26 will be described.

[0113] First, the reference antenna 3 is removed from the flat ground 1,
and then, the slit-like opening 11 is formed at the position where the
reference antenna 3 has been installed as depicted in FIG. 10; the
central portion of the dielectric plate 12 is buried in the slit-like
opening 11 such that the opposite end portions of the dielectric plate 12
are located at the opposite ends of the slit-like opening 11 (step ST24).

[0114] At this time, the conductor plates 13, 14 each electrically
connected to ground at the one end are placed so as to sandwich the
dielectric plate 12.

[0115] Then, the measured antenna 16 is installed on the dielectric plate
12 (step ST25). When the measured antenna 16 is installed on the
dielectric plate 12, the network analyzer 4 measures a frequency
characteristic E_dut(f) of a transmission characteristic between the
measured antenna 16 and the measuring antenna 2, similarly to the above
Embodiment 1 (step ST26).

[0116] Next, a calculation process of steps ST27 and ST28 will be
described.

[0117] When the frequency characteristic E_ref(f) of the transmission
characteristic between the reference antenna 3 and the measuring antenna
2, and the frequency characteristic E_dut(f) of the transmission
characteristic between the measured antenna 16 and the measuring antenna
2 are measured, similarly to the above Embodiment 1, the calculation
apparatus 4a calculates the frequency characteristic heff(f) in the
effective height of the measured antenna 16 by substituting the frequency
characteristic E_ref(f) and the frequency characteristic E_dut(f) into
the above Expression (1) (step ST27).

[0118] Upon calculating the frequency characteristic heff(f) in the
effective height of the measured antenna 16, similarly to the above
Embodiment 1, the calculation apparatus 4a calculates a frequency average
value heff_average in the effective height using the above Expression (2)
(step ST28).

[0119] In this case, the network analyzer 4 and the calculation apparatus
4a perform a similar measurement while the frequency of a radio wave
supplied to the measuring antenna 2 (prescribed frequency) is varied, and
average the frequency characteristic heff(f) in the effective height at
the prescribed frequency. As the prescribed frequency, for example, the
one of 500 MHz to 1500 MHz is used.

[0120] The measuring antenna 2 that is the monopole antenna installed on
the flat ground 1 radiates a polarized wave perpendicular to the flat
ground 1, and a high frequency propagate along the flat ground 1.
Therefore, when the measuring antenna 2 and the measured antenna 16 are
installed as depicted in FIG. 10, the polarized wave perpendicular to the
flat ground 1 can be irradiated to a side surface of the measured antenna
16, similarly to a case where a G-TEM cell is used.

[0121] As a result, the procedure illustrated in steps ST21 to ST28
enables an evaluation that is equivalent to that in the case where the
G-TEM cell is used.

[0122] In Embodiment 3, there is illustrated the case in which the single
measuring antenna 2 is installed to be separated by the predetermined
distance from the slit-like opening 11; however, similarly to the case in
which the N measuring antennas 2 are provided in the above Embodiment 2,
the N measuring antennas 2 may be provided around the slit-like opening
11, and the measured antenna 16 may be installed on the dielectric plate
12.

[0123] In this case, similarly to the above Embodiment 2, when a frequency
characteristic E_ref_i(f) of a transmission characteristic between the
reference antenna 3 and the N measuring antennas 2 is measured, and also
a frequency characteristic E--dut_i(f) of a transmission
characteristic between the measured antenna 16 and the N measuring
antennas 2 is measured, the frequency characteristic heff(f) in the
effective height of the measured antenna 16 and the frequency average
value heff_average in the effective height of the measured antenna are
calculated.

Embodiment 4

[0124] FIG. 12 is a perspective view depicting a partial discharge sensor
evaluation apparatus according to Embodiment 4 of the present invention.
In FIG. 12, the same reference numerals as those in FIG. 5 designate
identical or corresponding portions, and explanations thereof will be
thus omitted.

[0125] A radio wave absorber 31 is a pyramidal radio wave absorber
installed around a flat ground 1.

[0126] FIG. 12 depicts an example where the radio wave absorber 31 is
installed with respect to the partial discharge sensor evaluation
apparatus illustrated in the above Embodiment 1. However, the radio wave
absorber 31 may be installed with respect to the partial discharge sensor
evaluation apparatus illustrated in the above Embodiments 2 and 3.

[0127] When the transmission characteristic is measured using any of the
partial discharge sensor evaluation methods illustrated in the above
Embodiments 1 to 3, scattering waves from an edge portion of the flat
ground 1 may become an error factor.

[0128] In Embodiment 4, the radio wave absorbers 31 are arranged along the
edge portion in order to reduce the scattering waves from the edge
portion of the flat ground 1.

[0129] As a result, the error factor resulting from the scattering waves
from the edge portion can be reduced, which makes it possible to enhance
measurement accuracy in an effective height of antenna.

[0130] In Embodiment 4, there is illustrated the example where the
pyramidal radio wave absorbers 31 are installed around the flat ground 1.
However, as depicted in FIG. 13, a radio wave absorber 32 may be applied
at a periphery of the flat ground 1, which produces a similar
advantageous effect.

[0131] In Embodiment 4, there is illustrated the example where the
pyramidal radio wave absorbers 31 are installed around the flat ground 1.
However, as depicted in FIG. 14, a cut 33 may be provided on an edge
portion at the periphery of the flat ground 1.

[0132] The cut 33 provided on the edge portion causes the scattering waves
to be dispersed in various directions, and thus, the error factor
resulting from the scattering waves from the edge portion can be reduced,
which makes it possible to enhance the measurement accuracy in the
effective height of antenna.

[0133] In Embodiment 4, there is illustrated the example where the
pyramidal radio wave absorbers 31 are installed around the flat ground 1.
However, as depicted in FIG. 15, the edge portion at the periphery of the
flat ground 1 may be curved toward a side opposite to the measuring
antenna 2. 34 designates a curved surface of the edge portion.

[0134] Waves propagating on the flat ground 1 have the property of
propagating along the curved surface 34, which makes it possible to
scatter a radio wave in an area that is out of sight from the measured
antenna 9 and/or the measuring antenna 2. As a result, the amount of
scattering waves reaching the measured antenna 9 or the measuring antenna
2 is reduced, which makes it possible to enhance the measurement
accuracy.

[0135] In the present invention, the embodiments may be freely combined
with one another, any components of the embodiments may be varied, or any
components of the embodiments may be omitted without departing from the
scope of the present invention.

INDUSTRIAL APPLICABILITY

[0136] The partial discharge sensor evaluation method according to the
present invention is suitable for a case where it is necessary to achieve
downsizing of an apparatus used in detecting a high frequency generated
in an apparatus of a high-power facility such as a GIS to thus detect a
partial discharge phenomenon.